Hydrogels have been recently attracting attention from the viewpoint that hydrogels are soft materials having high biocompatibility because of containing water as the main component and having a low environmental load.
As a high-strength hydrogel having a self-supporting property, an organic/inorganic composite hydrogel is described that is obtained by performing a polymerization reaction of a (meth)acrylamide derivative in the coexistence with a layered clay mineral that is uniformly dispersed in water (Patent Document 1). As a similar example described, an organic/inorganic composite hydrogel is also known that contains a polymer partially containing a group of a carboxylate salt or a carboxy-anion structure in poly(meth)acrylamide and a clay mineral (Patent Document 2).
In these examples described, monomers are polymerized in an aqueous dispersion of a layered clay mineral, thereby causing a generated polymer and the clay mineral to form a three-dimensional network structure, which forms the organic/inorganic composite hydrogels.
However, the organic/inorganic composite hydrogels can leave unreacted monomers that may be toxic and reagents such as a polymerization initiator in the gels. It is difficult for non-chemical manufacturers to produce organic/inorganic composite hydrogels. It is also difficult to mold gels into a desired shape because hydrogels are formed after chemical reactions.
As an organic/inorganic composite hydrogel having a self-supporting property which can be produced through mixing at a room temperature, a hydrogel containing a dendrimer compound having a polycationic functional group at its terminal and a layered clay mineral has been known (Patent Document 3). In this example, the dendrimer is produced through multiple stages of synthetic reactions, and thus the production cost is high.
Also, an organic/inorganic composite hydrogels that can be prepared only by mixing a polyelectrolyte, clay particles, and a dispersant have been described (Non-Patent Document 1). In the organic/inorganic composite hydrogel, clay particles uniformly dispersed in a polyelectrolyte are cross-linked to form a gel structure. However, the gel is swollen in water, and thus strength and a shape cannot be maintained.
In addition, a gelation technique using a polyacrylic acid and an aluminum compound has been known (Patent Document 4). In this technique, the polyacrylic acid is cross-linked by aluminum ions to form a gel, and the gel is utilized as the plaster of cataplasms. This gel is gummy, and has excellent stickiness and flexibility; however, modulus of elasticity of the gel is low, and strength of the gel is not enough to maintain a shape against strong force.